There are only a few SS amps that are worth the extra $$$ over the prices of the X-250. In the right system, the X-250 could be the last amp you'll need or want. I have not heard the .5 but hear there that it is an improvement and you know that manufacturers and dealers need to move inventory to make a buck so that is why you are seeing the older models up for sale. I owned one for a long time and could not really find any big faults with the amp for the price I paid for mine. It does many things very well and was a work horse in my system with whatever front end and preamp I threw at it. If you want a SS amp and for the used prices they are being sold for, they are a bargain. Plus Pass Labs is a great company to do business with even if you are not the original owner and have a problem with one. Hook one up to an Elrod Sig 3 and sit back and enjoy. Here is the review of the amp I placed on AudiogoN a while ago. Bound for Sound did a review of the X-250 that was spot on also.
Pass X-250
Pass X-250